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// Copyright 2013 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef REMOTING_PROTOCOL_PAIRING_AUTHENTICATOR_BASE_H_
#define REMOTING_PROTOCOL_PAIRING_AUTHENTICATOR_BASE_H_
#include "base/macros.h"
#include "base/memory/weak_ptr.h"
#include "remoting/protocol/authenticator.h"
#include "third_party/libjingle_xmpp/xmllite/xmlelement.h"
namespace remoting {
namespace protocol {
// The pairing authenticator builds on top of V2Authenticator to add
// support for PIN-less authentication via device pairing:
//
// * If a client device is already paired, it includes in the initial
// authentication message a Client Id and the first SPAKE message
// using the Paired Secret and HMAC_SHA256.
// * If the host recognizes the Client Id, it looks up the corresponding
// Paired Secret and continue the SPAKE exchange.
// * If it does not recognize the Client Id, it initiates a SPAKE exchange
// with HMAC_SHA256 using the PIN as the shared secret. The initial
// message of this exchange includes an an error message, which
// informs the client that the PIN-less connection failed and causes
// it to prompt the user for a PIN to use for authentication
// instead.
// * If, at any point, the SPAKE exchange fails with the Paired Secret,
// the endpoint that detects the failure initiates a new SPAKE exchange
// using the PIN, and includes an error message to instruct the peer
// to do likewise.
//
// If a client device is not already paired, but supports pairing, then
// the V2Authenticator is used instead of this class. Only the method name
// differs, which the client uses to determine that pairing should be offered
// to the user (see NegotiatingHostAuthenticator::CreateAuthenticator and
// NegotiatingClientAuthenticator::CreateAuthenticatorForCurrentMethod).
class PairingAuthenticatorBase : public Authenticator {
public:
PairingAuthenticatorBase();
~PairingAuthenticatorBase() override;
// Authenticator interface.
State state() const override;
bool started() const override;
RejectionReason rejection_reason() const override;
void ProcessMessage(const buzz::XmlElement* message,
const base::Closure& resume_callback) override;
std::unique_ptr<buzz::XmlElement> GetNextMessage() override;
const std::string& GetAuthKey() const override;
std::unique_ptr<ChannelAuthenticator> CreateChannelAuthenticator()
const override;
protected:
// Create a Spake2 authenticator in the specified state, prompting the user
// for the PIN first if necessary.
virtual void CreateSpakeAuthenticatorWithPin(
State initial_state,
const base::Closure& resume_callback) = 0;
// A non-fatal error message that derived classes should set in order to
// cause the peer to be notified that pairing has failed and that it should
// fall back on PIN authentication. This string need not be human-readable,
// nor is it currently used other than being logged.
std::string error_message_;
// The underlying SPAKE2 authenticator, created with either the PIN or the
// Paired Secret by the derived class.
std::unique_ptr<Authenticator> spake2_authenticator_;
// Derived classes must set this to True if the underlying authenticator is
// using the Paired Secret.
bool using_paired_secret_ = false;
private:
// Helper methods for ProcessMessage() and GetNextMessage().
void MaybeAddErrorMessage(buzz::XmlElement* message);
bool HasErrorMessage(const buzz::XmlElement* message) const;
void CheckForFailedSpakeExchange(const base::Closure& resume_callback);
base::WeakPtrFactory<PairingAuthenticatorBase> weak_factory_;
DISALLOW_COPY_AND_ASSIGN(PairingAuthenticatorBase);
};
} // namespace protocol
} // namespace remoting
#endif // REMOTING_PROTOCOL_PAIRING_AUTHENTICATOR_H_
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